In the state of the art, devices are known for the transmission of parameters such as temperature, pressure, humidity, strain, etc. which can convert these parameters into strings of data that are then transmitted wireless, for example via radio signals.
These wirelessly transmitting devices usually comprise a transmitting arrangement in order to deliver over the air strings of data, which includes at least one value of a parameter measured by an associated sensor, to an associated receiver adapted to decode such data strings. The communication between the transmitter and the receiver occurs through a specific technique of modulation, and known modulations used in this type of devices are amplitude-shift-keying (ASK), frequency-shift-keying (FSK) and phase-shift-keying (PSK) modulation.
The main reason to adopt a wireless communication architecture on these devices is the possibility to deploy them anywhere, such as in rotating or vibrating structures or in locations that cannot be accessed during normal use or wherever it is not possible or feasible to implement a wired transmission.
A typical application example of these transmitting wireless devices is the maintenance of road vehicles. Recently, with the development of telemetry, systems have been developed for the automatic measurement and/or analysis of vehicle parameters and in particular also of parameters related to tires, such as pressure (Tire Pressure Monitoring System—TPMS).
However, these systems are not used regularly by vehicle operators, since they require high power consumption, due the continuous power supply of the electronic components involved, which must be ensured in order to be able to monitor these parameters.
In fact, due to the absence of wires, supplying sufficient energy to these devices for guaranteeing the transmission of all necessary information and a good reception of the wireless signals is normally a problem that affects the known devices for wirelessly transmitting measured parameters.
For this reason, in the approaches generally adopted for the hardware design of these devices, one of the main problems to be addressed is related to their energy efficiency: a high energy consumption, which may be required for a reliable wireless transmission, would make these devices unusable and uncomfortable in normal operating conditions, because they would be operative only for a short period of time, making it necessary to replace their battery often or even to replace the device itself. While these replacement operations may not be acceptable in normal operating conditions, they become completely unfeasible when the devices are mounted in locations which cannot be normally accessed, such as the inside of a tire.
Such a disadvantage is due to the fact that the known devices for wireless transmission of measured parameters are powered by means of energy sources having some capacity limits. These energy sources can be lithium cells, i.e. an exhaustible battery, that may have a diameter size that ranges between 24 and 48 millimeters.
Furthermore, in a wirelessly transmitting device powered by an exhaustible battery, the size of the battery itself affects the overall mechanical dimensions of the device: the mechanical form factor of this device is directly dependent to the density of the lithium cells, or more in general of the battery, that is measured in cubic centimeters.
In another arrangement, the battery cells of the wirelessly transmitting devices are replaced by energy harvesters, usually smaller than batteries. In this case, even though the power supply is potentially inexhaustible, the overall energy efficiency of the device becomes relevant, since the available power is low or relatively limited.
In other specific areas, the transmitting wireless devices are of “passive” type, wherein energy is supplied by the electromagnetic field generated by an associated electronic reader and the devices are arranged so as to exploit this inductive electromagnetic field to supply the internal electronic circuitry in response to a modulated radio frequency. However, in this case a high energy is demanded to the reader, which results in an overall inefficient system.